Pneumatic applicators are used in seeding and fertilizing. Generally, such applicators consist of a pressurized hopper with a metering device in its lower end for the controlled feeding of granular material from the hopper into a main conduit extending from a fan to a primary distributing header. Branch lines run from the primary header to secondary headers which in turn feed seed boots associated with ground breakers. The pneumatic pressure of the fan creates an air stream which carries the granular material from the metering device to the primary and secondary headers and then to the individual seed boots via a network of flexible hoses.
Conventional pneumatic seeders and fertilizer applicators have problems in maintaining an acceptable distribution of seed or fertilizer across the width of the machine. This is due mainly to the fact that the granular material does not reach the primary header in a centered, accurate stream. While it is generally understood that a co-efficient of variation (C.sub.v) of 15% across the width of the machine or spreading width is acceptable, this may be unacceptable to the farmer if one portion of the machine is applying a higher or leaner rate than another section.
As an example, primary distributing headers have anywhere from two to twelve dividing spouts or openings. If three openings are used on a header with a 15% variation between two of the openings, there would be an application rate difference from one section of the machine to another that would visually affect crop growth and yield.
It is therefore important to maintain a co-efficient of variation of less than 15% with an objective of achieving less than 5%.